1. Field of the Invention
This invention relates to a fluorescent display device comprising a cathode, and anodes and control electrodes arranged opposite to the cathode, and more particularly to a fluorescent display device including anodes each having a phosphor layer deposited thereon and control electrodes which are alternately arranged in a pectinate pattern on one surface of a substrate.
2. Description of the Prior Art
A fluorescent display device which has been conventionally used is typically constructed in such a manner to encapsulate anodes each formed into a desired character or figure shape and having a fluorescent material depositied thereon, a filamentary cathode arranged opposite to the anodes and grid-like control electrodes interposed between the anodes and the cathode in a transparent evacuated envelope, so that electrons emitted from the cathode impinge on the desired anodes to accomplish luminous display of desired characters or figures.
However, the conventional fluorescent display device has a disadvantage of substantially decreasing in luminance to render the observation of display from the cathode side difficult, because the control electrodes are interposed between the anodes and the cathode to obstruct the visual field when viewing display through the cathode.
Also, the conventional fluorescent display device includes display sections of plural digits for displaying characters or the like, each of which generally consists of a plurality of segments, and the control electrodes are arranged in a lump for every display section. Thus, even when causing only one of the segments of each display section to emit light, it is necessarily required to apply positive potential to all the control electrodes for the display section of one digit. This causes electrons to flow into all the control electrodes for the display section of one digit.
In this instance, the use of a segment scanning method for a dynamic driving operation of a fluorescent display tube often causes positive potential to be applied to the control electrodes for the display sections of all digits, for example, when the respective display sections carry out display of the same figure. This causes electric current flowing into the control electrodes to substantially increase, resulting in the cathode being eroded. Thus, in the conventional display device, the segment scanning method is hindered from being put into practice.
In view of the foregoing, the conventional fluorescent display tube is obliged to adopt a digit scanning method. However, the digit scanning method, depending upon its scanning manner, has a disadvantage that when the number of digits increases, for example, as in a bar display, the overall luminescence of display decreases because it is impossible to obtain sufficient duty ratio of display. In addition, the digit scanning method has another disadvantage of decreasing the utilization factor of electric power to cause the increase of power consumption because electric current flowing into the control electrodes is reactive current which never contributes to light emission.